Engine temperature closely relates to engine performance. During engine operation, engine temperature is monitored and controlled to ensure high fuel efficiency, reduced exhaust emission, and reduced friction loss. During engine cold start, fuel enrichment and/or spark retardation may be implemented in order to activate exhaust catalyst. During engine and transmission warm-up, high viscosity of lubricants causes increased friction. As a result, fuel consumption and exhaust emissions may be negatively impacted at low powertrain temperature. Accordingly, various approaches have been developed to reduce thermal losses from the powertrain.
One example approach is shown by Linden in U.S. Pat. No. 4,924,818. Therein, the engine or engine components are surrounded by a radiant heat retardant material to maintain the engine near operating temperatures for extended periods of time after engine shutdown, so that engine may start at a higher temperature in the subsequent restart.
However, the inventors herein have recognized potential issues with such systems. As one example, the heat retardant material may degrade or lose integrity over time. As another example, thermal encapsulation material may be removed for access to the powertrain during service, and the material may be damaged or the technician may fail to replace some pieces, causing degradation of the encapsulation system. The degradation may result in the loss of its ability to retain engine heat. Vehicle performance may further be impaired if the engine is operated with parameters configured under intact engine insulation.
In one example, the issues described above may be addressed by a method for diagnosing degradation of a thermal encapsulation positioned around a powertrain of a vehicle. The method comprising: sampling a temperature, via a sensor positioned onboard a vehicle driven by a powertrain having an engine, during an engine off condition; and indicating degradation of a thermal encapsulation positioned at least partially around the powertrain responsive to a temperature difference between the sampled temperature and an expected temperature. In this way, thermal encapsulation degradation may be promptly identified and addressed.
As one example, a vehicle powertrain may be configured with a thermal encapsulation device. For example, each powertrain component, including the engine and the transmission, may include one or more insulating units. An actual temperature of a powertrain component may be sampled via one or more existing sensors (such as, coolant temperature sensor, transmission oil temperature sensor, engine oil temperature sensor, and air inlet temperature sensor) during engine off condition. The sampled temperature from each sensor may be curve fitted and compared with an expected temperature profile to generate a temperature difference. In one example, the expected temperature may be generated from a powertrain with the thermal encapsulation, and a threshold may be generated from a prototype powertrain without one or more pieces of the thermal encapsulation. In another example, the expected temperature may be generated from a powertrain without thermal encapsulation. Degradation of the thermal encapsulation may be determined by comparing the temperature difference with the threshold.
As another example, actual temperature of a powertrain component may be sampled via one or more existing sensors (such as, coolant temperature sensor, transmission oil temperature sensor, engine oil temperature sensor, and air inlet temperature sensor) during engine on conditions in addition to or instead of during engine off conditions. Temperature differences between the sampled temperature and an expected temperature for each sensor under each operating condition may be calculated. Degradation of the thermal encapsulation material may be calculated based on a weighted average of the temperature differences, wherein each temperature difference may be weighted based on location of the sensor and the operating condition. Some types of degradation of or damage to the thermal encapsulation system may be more reliably detected during engine warm-up (engine on) than during engine cool-down (engine off).
In this way, thermal encapsulation degradation may be timely identified and addressed. By comparing a sampled actual temperature with an expected temperature, engine temperature excursions resulting from damage or loss of the encapsulation can be reliably identified using existing engine sensors. By sampling the temperature during engine off condition, effectiveness of the thermal encapsulation device is directly measured, and an accurate diagnosis of thermal encapsulation may be achieved. By calculating temperature differences based on multiple sensors under multiple operating conditions, thermal encapsulation degradation may be robustly determined. If degradation of the thermal encapsulation is detected, the system sets a diagnostic fault code and may turn on the Malfunction Indicator Light (MM).
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.